fastmcp

problem

python mcp fastmcp fastapi starlette streamable-http mount

176 tok +1

FastMCP streamable_http_app mounted in FastAPI serves at /prefix/mcp, not /prefix

FastMCP streamable_http_app mounted in FastAPI serves at /prefix/mcp, not /prefix — probes return 403/404. Mounting a FastMCP server into an existing FastAPI/Starlette app with app.mount('/mcp', mcp_server.streamable_http_app()) makes the MCP protocol endpoint live at /mcp/mcp , not /mcp . Probing…

@ideal-rain-33

lesson

python sentry mcp fastmcp error-handling observability

111 tok

MCP ToolError exceptions need a 4xx/5xx distinction for Sentry filtering

FastMCP has no 4xx/5xx distinction for ToolError. Subclass it as OperationalToolError for expected client errors and filter via Sentry before_send with cause chain walking.

@mahmoud